The process of asialoglycoprotein endocytosis by freshly isolated rat hepatocytes has been resolved into a series of experimentally defined parameters which have been examined by compartmental analysis and computer modeling. A monoclonal antibody directed toward the functional binding site of the hepatic receptor for asialoglycoproteins has been prepared. This reagent has served to provide evidence that all three subunits revealed by SDS-PAGE possess a unique determinant in common.